This invention relates to electrochemical cells including secondary cells and electroplating cells, and to an electrolyte having an additive for use therein to support interchangeable use of the electrolyte between different electrochemical cells.
A disadvantage encountered in electrochemical cells used in electroplating processes concerns the unequal deposition of metal on the surfaces of the negative electrodes. Generally, a higher current density occurs at projections on the surfaces of the negative electrodes leading to a buildup of metal crystals in these areas. This disadvantage is conventionally addressed by the addition of small quantities of smootheners or brighteners to the electrolyte of the electroplating cell. These can include natural gums and resins or synthesized compounds and mixtures which have similar plating properties. Other additives are typically also used to promote the plating process.
In the case of secondary electrochemical cells such as lead acid battery cells, for example, deposition of metal ions on the negative electrodes generally lead to reduced performance and, in extreme cases, battery failure. However, in battery cells the use of property altering additives is discouraged as these are believed to detrimentally affect battery performance. One would not use an electrolyte formulated with additives for electroplating use in a lead acid battery.
Some additives have been proposed for use, for example in zinc-alkaline batteries. For example, a quaternary ammonium polymer has been proposed in U.S. Pat. No. 3,660,170 to Rampel, in respect of a rechargeable battery, and an electroplating cell to inhibit the formation of excessive dendritic zinc on the negative plates of these cells. However, there is no suggestion for preparation of an interchangeable electrolyte.
Some quaternary ammonium polymers were proposed in U.S. Pat. No. 3,877,993 to Davis, for use in dry cells to reduce the stand deterioration of the negative plates of these cells. A quaternary ammonium monomer was proposed in U.S. Pat. No. 3,928,066 to Lewenstein, for use in conventional lead-acid batteries to inhibit the evolution of hydrogen gas from the negative plates and thereby attenuate the loss of water from these batteries. Again, no suggestion on preparation of an interchangeable electrolyte is found, From the prior art, it appears that various electrolytes are known for use in electroplating and other electrolyte formulations are known for use in battery cells. While suggesting a modification of the characteristics prevailing at the surfaces of the negative electrodes of these electrochemical cells, none of these prior art measures appear to provide an electrolyte formulated with an additive which is suitable for use in preventing deposition of metal ions emanating from the positive electrode of the cell in a way suitable for both electroplating cells and battery cells, such that the electrolyte is interchangeable between these cells. While sharing some components, each electrolyte is typically tailored to the to specific end use. To date, there is no interchangeable electrolyte that can be used, for example, in a battery cell and subsequently in an electroplating cell. Presently, spent battery electrolyte is considered a waste product. Utilizing an interchangeable electrolyte could provide opportunities for re-use and promote economically justified recycling of battery electrolyte.
According to the invention there is provided an electrochemical cell comprising a positive electrode, an opposed negative electrode, an aqueous electrolyte in ionic contact with a negative electrode, and a deposition modifying agent for inhibiting electrodeposition on the negative electrode of metal ions emanating from the positive electrode thereby to reduce or inhibit mass gain of the negative electrode.
According to the invention, an interchangeable electrolyte has been provided which can be used in battery cells as well as electroplating cells. The interchangeability is achieved by incorporating a surface active deposition modifying additive that renders the electrolyte interchangeable, while further enhancing battery life during battery use, and promoting smooth plating in an electroplating cell.
In both uses, surface effects appear to be the key to interchangeability. In a battery cell, metal deposition has been shown to limit battery life, while in an electroplating cell, deposition is to be promoted, not avoided. Thus, it would normally be considered impossible to provide an electrolyte suitable for both uses. Surprisingly, the deposition modifying additives of the invention, while inhibiting dendritic growth in a battery cell electrolyte, also support smooth plating when the same electrolyte is used in an electroplating cell, such that spent battery acid could be re-used in an electroplating cell. While the mechanism is not completely understood, it appears that the additive in each case promotes more organized deposition, which in the case of a battery cell, limits dendritic growth, increasing battery life, and in the case of an electroplating cell, promotes a smooth even finish. Thus, an electrolyte containing the additive is interchangeable in use, both when fresh or when recycled.
According to the invention, an interchangeable electrolyte contains a deposition modifying agent which is preferably of a type which is ionic in nature and which is attracted to the surface of the negative electrode, thereby preventing or inhibiting deposition on the negative electrodes of metal ions originating from the positive electrode when attracted in normal operation to the negative electrode.
The deposition modifying agent may preferably include a polar aspect and a non-polar aspect so as to have an affinity for water as well as oils, fats and the like. Furthermore, the non-polar aspect preferably includes an alkyl substituent, which provides a barrier to ions originating from the positive electrode.
The electrochemical cell is preferably a secondary cell, such as a lead acid battery cell, for example, or an electroplating cell, such as a tin electroplating cell, for example. The electrochemical cell may also be a gel electrolyte battery cell.
The combination of electrolyte and deposition moderating agent provides an electrolyte which is interchangeable between the secondary cell and the electroplating cell on an equivalent volume basis or by concentration or dilution thereof until it reaches the required or optimum specific gravity for use in the secondary cell or electroplating cell, as the case may be.
In the case of a lead or tin electrode battery having a sulfuric acid electrolyte, n-alkyl dimethyl benzyl ammonium chloride and sodium dioctyl sulphosuccinate have been shown to be effective to inhibit deposition on these electrodes, to enhance battery life, yet the sulfuric acid electrolyte dosed with either one of these additives can as well, whether fresh or in a spent condition, be used interchangeably in, for example, a tin electroplating cell.
The invention extends to a method of providing an interchangeable electrolyte for use in electroplating and battery electrochemical cells comprising providing an electrolyte, adding to the electrolyte a deposition modifying agent, which is compatible with the components of the battery and electroplating electrochemical cells, being non-reactive or slowly reactive with the electrolyte and capable of being attracted to the negative electrode in order to inhibit or prevent dendritic deposition thereon of metal ions emanating from the positive electrode which are attracted to the negative electrode, and promoting smooth electroplating on the electroplating cell surface.
The invention also extends to an electrochemical cell having a deposition modifying agent deposited on a component of the cell operatively in contact with an electrolyte placed in the cell so that, when an electrolyte is added to the cell, the deposition inhibiting agent associates with the electrolyte so as to be attracted to the negative electrode in order to inhibit or prevent deposition thereon of metal ions emanating from the position electrode which are attracted to the negative electrode during operation of the cell, the electrolyte after use being interchangeable and/or recyclable for use in a different electrochemical cell.